Role of surfactants in the control of dopamine-eumelanin particle size and in the inhibition of film deposition at solid-liquid interfaces.

Anionic and cationic surfactants such as sodium dodecylsulfate (SDS) and hexadecyltrimethylammonium bromide (HTAB) are able to control the size of "polydopamine" particles produced from dopamine solutions and to simultaneously strongly inhibit the deposition of "polydopamine" on surfaces. Indeed, dynamic light scattering experiments allowed to show that the hydrodynamic radius of polydopamine progressively decreases from about 1 μm to a few nanometer upon an increase in the SDS and CTAB concentration. At the highest surfactant concentration used (50 mM) the size of the aggregates is only slightly larger than the size of the surfactant micelles. On the other hand, the non-ionic Triton X-100 surfactant has no significant influence on both phenomena. It is suggested that the observed effect originates from the anionic and cationic surfactants acting as a template in which the growth of "polydopamine" is confined.